Title page for ETD etd-05202011-111953

Communication-constrained Feedback Stability and Multi-agent System Consensusability
in Networked Control Systems

Degree

Doctor of Philosophy (Ph.D.)

Department

Electrical & Computer Engineering

Advisory Committee

Advisor Name

Title

Zhou, Kemin

Committee Chair

Gu, Guoxiang

Committee Co-Chair

Wei, Shuangqing

Committee Member

Wolenski, Peter

Committee Member

Sathivel, Subramanian

Dean's Representative

Keywords

communication constrained feedback

multi-agent systems

consensusability

logarithmic quantizer

networked control systems

Date of Defense

2011-05-12

Availability

unrestricted

Abstract

With the advances in wireless communication, the topic of Networked Control Systems

(NCSs) has become an interesting research subject. Moreover, the advantages they offer

convinced companies to implement and use data networks for remote industrial control and

process automation. Data networks prove to be very efficient for controlling distributed

systems, which would otherwise require complex wiring connections on large or inaccessible areas. In addition, they are easier to maintain and more cost efficient. Unfortunately,

stability and performance control is always going to be affected by network and communication issues, such as band-limited channels, quantization errors, sampling, delays, packet

dropouts or system architecture.

The first part of this research aims to study the effects of both input and output quantization on an NCS. Both input and output quantization errors are going to be modeled as sector bounded multiplicative uncertainties, the main goal being the minimization of the quantization density, while maintaining feedback stability. Modeling quantization errors as uncertainties allows for robust optimal control strategies to be applied in order to study the accepted uncertainty levels, which are directly related to the quantization levels. A new feedback law is proposed that will improve closed-loop system stability by increasing the upper bound of allowed uncertainty, and thus allowing the use of a coarser quantizer.

Another aspect of NCS deals with coordination of the independent agents within a Multi-agent System (MAS). This research addresses the consensus problem for a set of discrete-time agents communicating through a network with directed information flow. It examines the combined effect of agent dynamics and network topology on agents' consensusability. Given a particular consensus protocol, a sufficient condition is given for agents to be consensusable. This condition requires the eigenvalues of the digraph modeling the

network topology to be outer bounded by a fan-shaped area determined by the Mahler